Caring waxes and loss wax technique

Question 1

What are boxing waxes?

Answer 1

used to retain the gypsum when it is poured into the impression

Question 2

What are beading waxes used for?

Answer 2

used to block out undercuts

Question 3

Qhy are waxes ideal?

Answer 3

can be moulded easily to the shape required

can be easily removed after gypsum has set

relatively inexpensive

Question 4

What temp can boxing and beading waxes retain their shape?

Answer 4

35 dc

Question 5

What are carving (presentation) wax good for?

Answer 5

diagnostic wax up, show patient

laid down in pt model

more easily visualised by pt

Question 6

What 2 material scanbe used for presentation wax?

Answer 6

inlay wax and carving wax

Question 7

Qhat wax is mainly used as the prototype?

Answer 7

inlay

Question 8

What technique is used for inlay wax?

Answer 8

lost wax technique

Question 9

constituents oif inlay wax

Answer 9

paraffin (60%)

ceresin

carnaba

candeilla

beeswax

Question 10

What are the 3 types of inlay waxes?

Answer 10

hard
medium
soft

Question 11

What is a positive of inlay waxes?

Answer 11

high level of detail and dimensional accuracy required

Question 12

What does stress releif lead to?

Answer 12

distortion of pattern and final resto will not fit

Question 13

What temp should you eat wax to?

Answer 13

45-50 dc

20 mins

Question 14

What colour are inlay waxes?

Answer 14

green, dark blue, purple

Question 15

When wold you use pattern waxes?

Answer 15

to construct the wax ‘framework’ which then forms the metal skeleton/baseplate

Question 16

What re the 2 types of inlay waxes?

Answer 16

prefabricated - in the shape of clasps etc

uniform thickness for the baseplate for a denture

Question 17

What are the properties of preformed wax patterns?

Answer 17

slightly sticky - can be repositioned on model

need to be very ductile

must burn out with no residue below the casting temp of the alloy used

Question 18

Why do you need to burn out wax?

Answer 18

no residue - no carbon incorporated in

Question 19

What does a baseplate/modelling wax form?

Answer 19

base of a denture

pink in colour

Question 20

What do you use the lost wax technique for?

Answer 20

fixed prosthodontic restorations:

inlays
onlays
crowns
bridges
removable prostheses

Question 21

What temp is the wax pattern designed to burn out at?

Answer 21

below 600dc

Question 22

What is the initial step in the lost wax technique?

Answer 22

wax pattern is made which corresponds to the shape of the object

Question 23

What is the goal of the lost wax technique?

Answer 23

wax form to metal tooth to be placed in pt mouth or denture

with similar features to the wax

Question 24

Describe what is going on here

Answer 24

wax pattern placed over DIE

sprue allows metal to flow in to the mould cavity - under high pressure

Question 25

What is the die?

Answer 25

tooth prepped for crown impression a model of an individual prepared tooth - DIE - this is a positive impression take impression and take to lab

Question 26

What is the crucible formed?

Answer 26

a structure which you place the sprue attached to the wax mould

Question 27

What has been placed over the crucible and wax casting?

Answer 27

casting ring open at top end

Question 28

what is placed inside the casting ring?

Answer 28

casting ring liner

Question 29

What gets brined out during burn out process?

Answer 29

casting ring liner wax

Question 30

Purpose of burnout phase?

Answer 30

not just a means to remove wax from the investment; it also cures the investment in preparation for the thermal shock of the metal entering the pattern cavity.

Question 31

What is the investment material?

Answer 31

form of alloy poured into casting ring - before burnout phase

Question 32

What is the purpose of the resevoir?

Answer 32

compensate of the cooling and contraction of the metal alloy that's started to cool

Question 33

What is the metal casting ring lined with?

Answer 33

piece of lining material aluminium silicate ceramic or cellulose lining paper liner

Question 34

What is the purpose of the lining material in the casting ring?

Answer 34

help to counteract the effects of the expansion of the investment during the heating phases

Question 35

Where should the wax pattern be situated in the casting ring?

Answer 35

hottest part of the ring (thermal centre) longest possible flow time

Question 36

What happens of the wax is to high up in the casting ring?

Answer 36

rupture the investment causing casting failure due to air moving through microporosities in the investment

Question 37

Do you wet the wax before placing in the casting ring?

Answer 37

sprayed with a wetting solution to reduce surface tension and prevent inaccuracies due to air entrapment

Question 38

What do you pour the investment into the casing ring on?

Answer 38

vibrating plate

Question 39

What are methods the alloy is heated?

Answer 39

naked flame e.g. oxyacetylene torch (if less than 1200 dc) or by using electric induction casting machine

Question 40

What alloys are quenched?

Answer 40

noble alloys becomes granular and causes it to fracture facilities burnishing and polishing

Question 41

What happens if the golf is left to cool?

Answer 41

harder, stronger casting results but this makes the alloy more difficult to finish

Question 42

When do you remove the casting form the alloy?

Answer 42

after cooling

Question 43

How do you remove surface oxides form the crown after removing the investment?

Answer 43

sandblasting

Question 44

What is the advantage of the lost wax process?

Answer 44

high level accuracy dimensional change less than 0.05%

Question 45

Why can the cast come out smaller than expected?

Answer 45

due to the mould not having been heated sufficiently

Question 46

Why may the casting be distorted?

Answer 46

can be due to the wax pattern being damaged during the investing process or by incorrect sprue placement preventing the metal flowing to the extremities of the mould

Question 47

How can you prevent distorting\/

Answer 47

thickening of the wax margins

Question 48

How would you melt base metal alloys?

Answer 48

electric induction heating melt at 1200-1500 dc

Question 49

What happens if the alloy is cooled quickly?

Answer 49

coring this is variable metals in the same alloy electrolytic metals and prone to corrosion/weakness

Question 50

How to overcome coring?

Answer 50

homogenisation treatment reheat alloy and cool slowly

Question 51

gaseous porosity?

Answer 51

dissolve oxygen when heated metal voids oxygen incorporated when alloy is heated/molten